I was told years ago I should stop cycling, because of the possibility of having a fit/seizure/episode/call it what you want whilst cycling. I countered with research has shown you are less likely to have one whilst doing something you like. The specialist acknowledged this to be true. I'm assuming your friend likes cycling.
I'm not able to say "I know what it feels like" as I've known no different. The fit/seizure/episode/call it what you want side I can understand. There's a period where I'll go through trying to work out what happened, but I've long since given up trying to work out what I could have done to prevent one in the first place. The best advice is to stay away from "Dr google", some of the stuff is bad enough to have me thinking twice. They can hurt like hell after, even with no visible injury.
Any concerns, they can speak to/get in touch with
https://www.epilepsy.org.uk or write any questions down before being seen, and work from the list when seen.
Don't let them saying "You can't do that!" put them off.